In recent years, optical camera shake correction (which may be also referred to as an optical image stabilizer (OIS)) has been adopted for a camera module incorporated in a smartphone or the like. A camera module with OIS includes a lens (also referred to as a camera shake correction lens) movable in a direction (XY plane) horizontal to an imaging surface of an imaging element. When blurriness is detected by a blur detecting part such as a gyro sensor, the lens is shifted so that the blurriness is canceled out.
FIG. 1 is a block diagram of a camera module with a camera shake correction function. A camera module 1000 includes an imaging element 1002, a lens 1004, an actuator 1006, an actuator driver 1008, a position detecting clement 1010, a blur detecting part 1012, and a CPU (Central Processing Unit) 1014.
The imaging element 1002 picks up an image transmitted through the lens 1004. The blur detecting part 1012 detects blurriness in an output from the camera module 1000. The actuator driver 1008 receives a signal D1 indicating the amount of blur detected by the blur detecting part 1012 and generates a target code indicating a target value of displacement of the lens 1004 so as to cancel out the blur. The actuator driver 1008 generates a drive signal S5 for the actuator 1006 based on the internally generated target code. The actuator 1006 positions the lens 1004 according to the drive signal S5.
Feedback control (closed-loop control) is adopted for the camera shake correction because it is necessary to accurately position the lens 1004. The position detecting element 1010 generates a position detection signal S2 indicating the displacement of the lens 1004. The actuator driver 1008 performs feedback control of the drive signal S5 so that the position of the lens 1004 indicated by the position detection signal S2 coincides with the target position indicated by the target code.
The actuator driver 1008 performs linear control between the angle blur amount calculated based on the output of the blur detecting part 1012 and the displacement of the lens 1004. Therefore, in the camera module 1000, it is important that linearity is secured between the detected displacement of the lens 1004 and the actual displacement. However, since it is difficult to guarantee perfect linearity between the position detection signal S2 generated by the position detecting element 1010 and the actual displacement of the lens 1004, correction is necessary.
In this connection, a technique is being developed using a correction function or a correction table to correct the nonlinearity of an output of a position detecting element in OIS. Other techniques are also being developed to compensate for a fluctuation in output of an OIS position detecting element caused by a change in temperature.
For such correction (hereinafter referred to as linear compensation), it is necessary to measure the relationship between the position detection signal S2 and the actual position of the lens 1004 in advance.
The displacement information of the lens 1004 in the direction of an optical axis (Z axis) can be measured by using a relatively inexpensive laser displacement gauge or the like, which may be, in many cases, installed in a manufacturing process.
In order to acquire displacement information in a direction (XY axis) perpendicular to the optical axis, which is necessary for control of optical camera shake correction by the laser displacement gauge, the lens 1004 must be irradiated with a laser from the direction perpendicular to the optical axis. In practice, however, since the side surface of the lens 1004 is covered with other members (not shown), it is difficult to measure the displacement of the lens 1004 with the laser displacement gauge.
There is also a displacement gauge that detects the displacement in the XY direction from the Z axis direction, but since it is necessary to install a dedicated target, it takes much time and labor for measurement. In addition, since this displacement gauge is expensive, the cost to obtain displacement information becomes high. A laser Doppler measuring instrument may also be used to measure the displacement in the XY direction, but it is similarly expensive.